Various wireless access technologies have been proposed or implemented to enable mobile stations to communicate with other mobile stations or with wired terminals coupled to wired networks. Examples of wireless access technologies include GSM (Global System for Mobile communications) or UMTS (Universal Mobile Telecommunications System) technologies, defined by the Third Generation Partnership Project (3GPP); CDMA 2000 (Code Division Multiple Access 2000) technologies, defined by 3GPP2; or other wireless access technologies.
Another type of wireless access technology is the WiMAX (Worldwide Interoperability for Microwave Access) technology. WiMAX is based on the IEEE (Institute of Electrical and Electronics Engineers) 802.16 standards. The WiMAX wireless access technology is designed to provide wireless broadband access.
One of the features provided by the WiMAX technology is support for MIMO (multiple input, multiple output). MIMO refers to use of multiple antennas at the transmit site and at the receive site, such that data can be transmitted from multiple antennas of a transmitter over multiple paths for receipt by antennas of a receiver. Usage of the MIMO technology enhances capacity, scalability, and flexibility of wireless networks. By using the MIMO technology, multiple parallel channels (in the form of multiple spatial beams or streams) can be provided to achieve increased capacity.
Closed loop MIMO (CL-MIMO) refers to a MIMO mode that uses information about the transmission channel that is fed back from the mobile station to a serving base station, where the base station uses the feedback information to select resources for use in wireless communications between the base station and the mobile station and to compensate for effects of the transmission channel. Conventionally, efficient feedback mechanisms have not been provided to enable closed loop MIMO operations.